From Jeff Masters.
'The last half of June is usually one of the quietest portions of hurricane season. In the 14 years since the current active hurricane period began in 1995, only four tropical storms formed in the last half of June. None of those four storms since 1995 became a hurricane, and hurricanes are quite rare in June.
Sea Surface Temperatures (SSTs) have remained close to average over the tropical Atlantic between Africa and Central America this month .
These are the coolest SST anomalies we've seen since 1994. The strength of the Azores-Bermuda high has been near average over the past two weeks, driving near-average trade winds. Stronger-than-average trade winds were observed through most of the period November 2008 - May 2009, which helped cool the tropical Atlantic substantially. Strong winds mix up colder water from the depths and cause greater evaporative cooling. The latest 2-week run of the GFS model predicts continued average trade winds over the tropical Atlantic for the remainder of June, so expect the near-average SSTs to continue over the tropical Atlantic as we head into July.
Typically, June tropical storms form over the Gulf of Mexico, Western Caribbean, and Gulf Stream waters just offshore Florida, where water temperatures are warmest. SSTs are 26 - 28°C in these regions, which is about 0.5°C above average for this time of year.
June storms typically form when a cold front moves off the U.S. coast and stalls out, with the old frontal boundary serving as a focal point for development of a tropical disturbance.
African tropical waves, which serve as the instigators of about 85% of all major hurricanes, are usually too far south in June to trigger tropical storm formation. SSTs are too cold in June to allow storms to develop between the coast of Africa and the Lesser Antilles Islands--there has only been once such development in the historical record--Ana of 1979, which coincidentally will be the name given to this year's first storm.'